Except of masking the unstable icu ebuilds as recommended from the devs I don't know how to handle the other blocks. Nor did I find anything related to my problems in the forums or at b.g.o ... anyone else has similar problems?

(media-libs/libjpeg-turbo-1.3.0::gentoo, installed) pulled in by
<media-libs/libjpeg-turbo-1.3.0-r2 required by (app-office/libreoffice-bin-4.0.4.2::gentoo, ebuild scheduled for merge)

(media-libs/libjpeg-turbo-1.3.0-r2::gentoo, ebuild scheduled for merge) pulled in by
>=media-libs/libjpeg-turbo-1.3.0-r2:0[static-libs?,abi_x86_32(-)?,abi_x86_64(-)?,abi_x86_x32(-)?,abi_x86_32(-)?,abi_x86_64(-)?,abi_mips_n32(-)?,abi_mips_n64(-)?,abi_mips_o32(-)?] required by (virtual/jpeg-0-r2::gentoo, ebuild scheduled for merge)
(and 1 more with the same problem)

Thanks for your reply MustrumR but it's a deliberate choice to use the -bin package since quite a few of my systems (laptops) are simply too weak to get through a compilation of the libreoffice package

I'm sorry, but libreoffice-bin package is meant only for stable users. The new multilib libjpeg-turbo doesn't work because it doesn't install the same file anymore as required only by libreoffice-bin in Portage tree. And if you use package.keywords to unmask random library that needs the multilib libjpeg-turbo as a dependency, the same problem is there again.
There might not be other sane option than switch.

Except if you are willing to settle for an hack. You can copy the libreoffice-bin ebuild to overlay, and remove the jpeg dependency from the ebuild completely, then you can get libjpeg.so.8 file from stable libjpeg-turbo, save it and copy it to /usr/local/lib and run `ldconfig`. Then you can upgrade to newer libjpeg-turbo and libreoffice-bin keeps working because the libjpeg.so.8 is in /usr/local/lib and it finds it because `ldconfig` was executed (as root).

I'm sorry, but libreoffice-bin package is meant only for stable users. The new multilib libjpeg-turbo doesn't work because it doesn't install the same file anymore as required only by libreoffice-bin in Portage tree. And if you use package.keywords to unmask random library that needs the multilib libjpeg-turbo as a dependency, the same problem is there again.
There might not be other sane option than switch.

Except if you are willing to settle for an hack. You can copy the libreoffice-bin ebuild to overlay, and remove the jpeg dependency from the ebuild completely, then you can get libjpeg.so.8 file from stable libjpeg-turbo, save it and copy it to /usr/local/lib and run `ldconfig`. Then you can upgrade to newer libjpeg-turbo and libreoffice-bin keeps working because the libjpeg.so.8 is in /usr/local/lib and it finds it because `ldconfig` was executed (as root).

Thanks ssuominen for that workaround!!! Even though being ugly it keeps my systems running without too much of an hassle

Without this particular hack, for sure, after packages get stabilized. But it doesn't change the fact that libreoffice-bin is only designed for stable users, and not built for ~arch users at all. That's the price you have to pay for using the latest and greatest. Other hacks will be needed in long run.